1. Field of the Invention
The present invention relates to the field of electronic packages, and more particularly, to the field of hermetically sealed electronic packages.
2. Background Information
For many applications, it is either desired or necessary to provide a hermetically sealed package for electronic devices. In the case of vacuum tubes, a hermetic seal is essential to the proper operation of the device. With semiconductor devices, a hermetically sealed package is considered necessary or desirable for semiconductor devices for which high reliability is required or which will be exposed to hostile environments. One of the problem areas in providing a hermetically sealed package is provision of hermetic seals between leads which extend from within the hermetically sealed portion of the package to outside the package enclosure. Over the years, many different lead and seal combinations have been developed in an attempt to provide hermetically sealed packages. These efforts have included the development of special metal alloys whose thermal coefficients of expansion are similar to that of the electrically insulating material through which the lead must pass along with the development of special sealing materials having substantially matched coefficients of thermal expansion such as special composition glasses for sealing the gap between the lead and the insulating body of the package.
One type of hermetically sealed package is disclosed in patent application Ser. No. 367,525, filed Jun. 16, 1989, entitled "Hermetic Package Having a Lead Extending Through an Aperture in the Package Lid and Packaged Semiconductor Chip", by V.A.K. Temple et al. In that package, apertures in a ceramic package lid are hermetically sealed by a direct bond between the ceramic lid and a copper foil which extends across an aperture in the lid. The direct bond copper process used to form this copper foil-to-ceramic seal or bond is described in U.S. Pat. Nos. 3,744,120, 3,854,892 and 3,911,553 to Burgess et al.; U.S. Pat. Nos. 3,766,634 and 3,993,411 to Babcock et al.; U.S. Pat. Nos. 3,994,430 and 4,129,243 to Cusano et al.; U.S. Pat. No. 4,409,278 to Jochym; and U.S. Pat. No. 4,563,383 to Kuneman et al. Each of these patents is incorporated herein by reference. These direct bond patents teach that copper-copper oxide, nickel-nickel oxide, cobalt-cobalt oxide, iron-iron oxide and copper-copper sulfide eutectics can be used to form bonds of this type. This bond is formed by a copper-copper oxide eutectic mixture which wets both metallic copper and ceramic materials such as alumina and beryllia and which bonds the members together upon solidification. This copper-copper oxide eutectic process has been in use for many years in the electronic arts.
As discussed in application Ser. No. 367,525, it has been found that the copper foil must be direct bonded to the ceramic over a distance of about 100 mils in order to ensure the formation of a hermetic seal. This places a limit on the minimum spacing between electrically isolated leads. For some applications, the resulting minimum center-to-center spacing of leads is a severe disadvantage. A variation on that package is the subject of patent application Ser. No. 375,636, filed Jul. 3, 1987, and entitled "Hermetic Package and Package Semiconductor Chip Having Closely Spaced Leads Extending Through the Package Lid" by V.A.K. Temple et al.
Application Ser. No. 375,636 substantially reduces the spacing required between adjacent leads as compared to application Ser. No. 367,525. However, the minimum center-to-center lead spacing is still greater than is desirable for many applications.
Consequently, there is a need for an improved hermetic seal between a ceramic package component and a lead passing therethrough which requires less package component area per lead.